refactor(macos): extract gateway payload decoding

apps/macos/Sources/Clawdis/GatewayPayloadDecoding.swift

@@ -0,0 +1,16 @@
+import ClawdisProtocol
+import Foundation
+
+enum GatewayPayloadDecoding {
+    static func decode<T: Decodable>(_ payload: ClawdisProtocol.AnyCodable, as _: T.Type = T.self) throws -> T {
+        let data = try JSONEncoder().encode(payload)
+        return try JSONDecoder().decode(T.self, from: data)
+    }
+
+    static func decodeIfPresent<T: Decodable>(_ payload: ClawdisProtocol.AnyCodable?, as _: T.Type = T.self) throws
+        -> T?
+    {
+        guard let payload else { return nil }
+        return try decode(payload, as: T.self)
+    }
+}

apps/macos/Sources/Clawdis/InstancesStore.swift

@@ -92,11 +92,7 @@ final class InstancesStore: ObservableObject {
         case .seqGap:
             Task { await self.refresh() }
         case let .snapshot(hello):
-            if JSONSerialization.isValidJSONObject(hello.snapshot.presence),
-               let data = try? JSONEncoder().encode(hello.snapshot.presence)
-            {
-                self.decodeAndApplyPresenceData(data)
-            }
+            self.applyPresence(hello.snapshot.presence)
         default:
             break
         }
@@ -264,8 +260,7 @@ final class InstancesStore: ObservableObject {
 
     func handlePresenceEventPayload(_ payload: ClawdisProtocol.AnyCodable) {
         do {
-            let payloadData = try JSONEncoder().encode(payload)
-            let wrapper = try JSONDecoder().decode(PresenceEventPayload.self, from: payloadData)
+            let wrapper = try GatewayPayloadDecoding.decode(payload, as: PresenceEventPayload.self)
             self.applyPresence(wrapper.presence)
         } catch {
             self.logger.error("presence event decode failed: \(error.localizedDescription, privacy: .public)")

apps/macos/Sources/Clawdis/WebChatSwiftUI.swift

@@ -213,8 +213,7 @@ final class WebChatViewModel: ObservableObject {
     private func handleGatewayEvent(_ evt: EventFrame) {
         guard evt.event == "chat" else { return }
         guard let payload = evt.payload else { return }
-        guard let data = try? JSONEncoder().encode(payload) else { return }
-        guard let chat = try? JSONDecoder().decode(ChatEventPayload.self, from: data) else { return }
+        guard let chat = try? GatewayPayloadDecoding.decode(payload, as: ChatEventPayload.self) else { return }
         guard chat.sessionKey == nil || chat.sessionKey == self.sessionKey else { return }
 
         if let runId = chat.runId, !self.pendingRuns.contains(runId) {